In this application the hypothesis is being tested that the myelin basic protein (MBP) gene is more complex than originally thought, and that parts of the gene are expressed in mRNAs that do not encode MBPs. We have evidence for the expression of an mRNA in oligodendrocytes which is encoded by a gene that either overlaps or forms a part of the MBP gene. This MBP gene-Cl related product is expressed in oligodendrocytes (or their precursors) and in the spleen. In the oligodendrocyte, these mRNAs are expressed according to a different developmental pattern than that of the majority of MBP mRNAs. The overall goal of this project is to examine the structure and organization of this gene, to determine its expression in oligodendrocytes, and to deduce the role it plays during oligodendrocyte differentiation through an examination of its expression in both oligodendrocytes and cells of the immune system. We propose to complete the isolation, characterization and analysis of these mRNAs for which we currently have isolated only 40% of the entire message. The structure of the gene will be determined with respect to its exon/intron structure and its structural relationship to the MBP gene. Preliminary evidence indicates that the gene is expressed in either immature oligodendrocytes or their precursor cells. Accordingly, the cell type and the developmental stage at which oligodendrocytes express the gene will be determined. Experiments also will be performed to disrupt expression of the gene with antisense oligodeoxynucleotides and examine the subsequent differentiation of the oligodendrocyte. The ontogeny of expression of the gene will be examined in vivo and in vitro in several immunologically relevant tissues and cell lines by in situ hybridization to determine the stage of B cell and T cell development at which expression occurs. The hypothesis being examined in these experiments and those dealing with oligodendrocyte differentiation is that the gene plays some role in the differentiation of the oligodendrocyte. We believe that it may be possible to elucidate the role of this gene in oligodendrocytes through an examination of its expression in the immune system, where B cell and T cell differentiation is well understood.